Cook bacon, then add onions and greens: Preheat oven to broil with rack about 10 inches from heat source. Heat bacon in a large, deep ovenproof skillet over medium. Cook, stirring occasionally, until bacon is crisp, about 7 minutes. Add onion; cook, stirring often, until softened, about 3 minutes. Add collard greens, stock, and 2 teaspoons paprika; bring to a simmer over medium, stirring and scraping bottom of skillet. Simmer, stirring occasionally, until greens are wilted, about 4 minutes.
Add tomato sauce and tortellini: Stir in marinara, and return to a simmer over medium-high. Add tortellini; cook, stirring occasionally, until tortellini begin to plump and soften, about 4 minutes.
Add cheeses and panko topping: Remove from heat; fold in 1 cup Cheddar or mozzarella. Sprinkle top with remaining ½ cup Cheddar or mozzarella. In a small bowl, stir together panko, Parmesan, olive oil, garlic, salt, and remaining ½ teaspoon paprika; sprinkle evenly over tortellini.
Broil: Broil until panko topping is golden brown, about 2 minutes.
