01 - Preheat oven to 375°F.
02 - Slice tops off bell peppers and remove seeds and membranes. Arrange upright in baking dish.
03 - Combine spinach, Parmesan, pine nuts, olive oil, garlic, salt, pepper, lemon zest, and oregano in food processor. Pulse until coarse pesto forms.
04 - Transfer pesto to bowl. Fold in cottage cheese until well combined.
05 - Fill each pepper generously with cottage cheese-spinach pesto mixture.
06 - Sprinkle mozzarella cheese on top if using.
07 - Add 2-3 tablespoons water to bottom of baking dish to prevent scorching.
08 - Cover dish with foil and bake for 25 minutes.
09 - Remove foil and bake additional 10 minutes until peppers are tender and tops are golden.
10 - Let cool slightly, garnish with fresh basil, and serve warm.