Ingredient suggestions:

the flour: this recipe is basically just holding itself together so you dont have a lot of lee way with the amount and it doesnt take very well to alternative flours. best to stick with 1 3/4 cup of all purpose flour, or if you like a stronger less crumbly quick bread you can add up to 1/2 cup more flour.

the oatmeal: this recipe is basically just holding itself together so you dont have a lot of lee way with the amount and it doesnt take very well to adjustments. More oatmeal and its too crumbly, too little and the texture suffers. best to stick with 1/4 cup oatmeal.

the leavening: using more baking powder will yield a fluffier bread, and more baking soda will make the bread a bit more dense and pound cake like. you should always stay between 2-3 tsp total, and more and its tastes off, any less and the bread is too dense and gummy.

the salt: just stick with a heavy pinch.

the spices: any and all spices will work in the dough, just bear in mind some taste much stronger than others. i would not go over 3 tsp total, and 2 would be a better amount to aim for as this recipe doesnt have as much sugar as a cake.

the fruit and veg: the amount should remain at 2 cups total as less and your bread is too dry, and more would mean it would never fully bake. other than that the fruit or veggies you use are almost endless, the only exclusions would be fruits that are almost pure water such as all of the melons. Any other fruits will work just make sure if using frozen they are thawed or peeled if need be. For veggies that are edible raw and have a high moisture content you can either shred or mash them, such as zucchini or tomatoes. For veggies that cant be eaten raw or arent what youd call high moisture such as carrots, sweet potatoes, or pumpkin, you will want to boil them until they are soft enough to be mashed. other than taht you can use any veggies you would like, and for both the fruits and veggies you can mix and match.

the oil: technically any liquid oil will work here as it is just adding fat and not structure. keep in mind the taste of the oil though, if you did pure olive oil it would over power and other flavor you tried to add. the amount should stay at 1/3 cup.

the sugar: any sugars, and in any combination will work except for powdered sugar since it has cornstarch in it. you can go as high as 1 1/3 a cup if you want a really sweet quick bread, or as low as 1/2 cup sugar if you want it to taste more naturally like the fruit. 2/3 a cup is a good middle ground. brown sugar will lead to a slightly more moist dough than regular sugar.

the added fat: the extra tbsp of butter in these recipes is solely for flavor, adding complexity to a simpler recipe. it can be completely omitted, or you can go as high as 2 tbsp but any more and your batter gets too dense. Any solid fat will work but may affect your final texture.

the acid: The addition of vinegar like the butter is partly to help with the flavor, but also to help the dough rise as a lot of these fruits and veggies can dampen the leavinings effects. any acid will work such as vinegars or lemon juices. You can go up to 1 1/2 tbsp if you would like more flavor, and as low as 1/2 tbsp. you can omitt this ingredient but the rise may suffer.

the zests: any fruit zest will work and will go into the wet ingredients. Since this batter does not usually have a lot of sucgar id stay around the amount of two lemons worth.

Topping suggestions: if desired the topping can be omitted entirely.

the sugar: if doing a topping you can go as low as 2 tbsp or as high as 6. Less makes the topping less sweet and you wont have as much to spread around, more and it will be sweeter but also have a crunchier mouth feel.

the oatmeal: this adds a nice flavor and crumbly texture to the topping. you can go as low as 2 tbsp or as high as 6 tbsp but keep in mind you add ore most of it is just going to slip off the top when you eat. making it as messier snack.

the liquid: the amount should never go over or under 1 tbsp as it will effect how the batter bakes on top. this is being used solely to help the topping stick and hold together. you can use any liquid you would want.

the spices: any spice can be used in the topping but dont let the amount go over 1/2 tsp as there isnt enough sugar here to combat a lot of spice.

THE ZEST: ANY CITRUS ZEST CAN BE USED IN THE TOPPING BUT I WOULDNT GO OVER 2 TBSP TOTAL OR IT MAY BE TOO STRONG OR BITTER AS TEH TOPPING DOES NOT HAVE A LOT OF SUGAR IN IT.