Crust: To a microwave-safe bowl, add shredded mozzarella and cream cheese and transfer bowl to microwave. Microwave on high for 1 minute. Mix cheese mixture with spatula and microwave again for additional 30 seconds.
Remove bowl from microwave, add egg, and mix until ingredients are well-combined. (If mixing becomes too difficult, return bowl to microwave and microwave on high for about 20 seconds. Mix again with a spatula.) To bowl, add ground sunflower seed meal and salt and, using hands, knead mixture together until fully incorporated. Cover bowl with foil and transfer to refrigerator to chill while preparing taco mixture, about 20-30 minutes.
Toppings: In a large pan over medium heat, cook ground beef until browned, about 5-10 minutes, breaking up the meat with a spatula as it cooks. Drain and discard excess fat. To pan, pour in water and add taco seasoning, tomato paste, and coconut aminos.
Return pan to burner over medium heat and simmer until sauce thickens, about 4-5 minutes. Remove pan from heat and set aside.
Preheat oven to 400 degrees.
Final Steps: Remove bowl of dough from refrigerator and transfer dough to parchment paper or silicone baking liner. Place another piece of parchment paper atop dough and, using a rolling pin, roll dough out to about ¼” thick. Remove and discard top piece of parchment paper. Carefully slide a baking sheet beneath the parchment paper with the dough on top. Using a fork, gently prick dough all over. Transfer baking sheet to oven and bake until golden, about 10-12 minutes.
Remove baking sheet with crust from oven. To top of crust, add salsa, then taco-seasoned ground beef, then sprinkle with shredded mozzarella and shredded cheddar. Return pizza to oven until cheese melts, about 5-10 minutes.
Remove baking sheet from oven and top pizza with shredded romaine, sour cream, and avocado slices.