PREHEAT oven to 375F. Cut out 12 5 × 5-in. squares of parchment. Press a parchment square into each cup of a 12-cup muffin pan, or spray with oil. CUT the crusts off bread slices. Use a rolling pin to flatten slices, then press slices into prepared cups to make shells. Spray tops with cooking spray. Toast in centre of oven, 5 to 7 min. MELT butter in a non-stick frying pan over medium. Add onion. Cook, stirring occasionally, until soft and brown, 12 to 15 min. Stir in maple syrup and spinach. Cook until spinach wilts, 1 to 2 min. Spoon some spinach mixture into each bread shell, sprinkle sun-dried tomatoes over spinach, and crack an egg on top. Season with salt and fresh pepper. BAKE in centre of oven until egg whites are set but yolks are runny, 15 to 18 min.