What traybake or muffins (sweet) are good for reducing sugar and high in fibre?

Ways to come up with a recipe for this challenge:
• most muffin recipes work well even when sugar amount is cut in half
• make a muffin recipe you already know that works & substitute a higher fiber veg or fruit for the original one (e.g., raspberries instead of bananas)
• add supplements (but not too much) to recipe...2 tbsp wheat bran or replace 1/4 of white flour volume with whole wheat flour

What is considered high fiber, and low sugar? I mean do you have quantitative limits you need to achieve?