1. Working with one noodle at a time, spread a scant two tablespoons of filling over noodle (it will not cover entire noodle).
2. Sprinkle some sautéed onion over each noodle and place three slices of tomato evenly across it.
3. Beginning with one long end, roll up noodle carefully. Slice rollup in half. Repeat with remaining noodles.
4. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Place 48 cupcake cups into muffin tins. Divide the marinara sauce between the cups, pouring some into the bottom of each cup until thickly coated.
5. Place half of a roll-up into each cup so that the curly sides face upward, forming “flowers.” Spray tops with cooking spray and cover tightly with aluminum foil.
6. Bake for 40 minutes. Allow to cool for five minutes before serving.
If you’d like a cheesier, saucier roll-up, you can add a bit of shredded cheese and sauce on top of the flowers when rewarming. Heat uncovered until cheese melts.