Heat ½ tbsp. olive oil in a skillet over medium heat. Sauté diced onions and minced garlic until fragrant.
Add ground chicken breast and cook, breaking it up with a spatula until no longer pink.
Stir in chili powder, cumin, garlic powder, paprika, oregano, onion powder, salt, pepper, and red pepper flakes. Cook for 5 more minutes.
While the chicken cooks, dice roma tomatoes and chop scallions.
Wash and pat dry romaine lettuce leaves, keeping them whole for wrapping.
Spoon the seasoned chicken onto lettuce leaves and top with cheddar cheese, avocado corn salsa, and plain Greek yogurt.
Garnish with scallions and extra toppings of choice.
Serve immediately and enjoy your fresh, flavorful keto tacos!