Preheat oven to 350°F (175°C). Lightly grease a 13x9 inch baking dish.
Thaw riced cauliflower completely and squeeze very dry in a clean towel, or sauté it in a dry skillet for 3 to 4 minutes to evaporate moisture. Cool.
Heat a large skillet over medium-high. Cook sausage, onion, and bell peppers for 8 to 10 minutes until sausage is browned and vegetables are soft. Stir in paprika, cumin, and black pepper for 30 seconds. Drain excess fat or liquid.
In a large bowl whisk yogurt with milk until smooth. Add eggs, salt, and flaxseed. Whisk until fully combined and slightly airy.
Optional but helpful: spread tortilla squares on a sheet pan and toast at 350°F for 5 to 7 minutes until just crisp.
Layer in dish: cauliflower, half the sausage mixture, 1 cup cheese, drained salsa, and cilantro. Scatter tortillas. Pour half the egg mixture evenly. Top with remaining sausage, then remaining egg mixture, then the last 3/4 cup cheese.
Cover tightly with foil and bake 35 minutes. Uncover and bake 25 to 30 minutes more until golden and the center reaches 160 to 165°F (71 to 74°C) or a knife inserted in the center comes out clean with only a slight jiggle.
Rest 10 to 15 minutes. Garnish with green onions and serve.