Preheat your air fryer to 350°F (175°C). If using an oven, preheat to 375°F (190°C) and line a baking sheet with parchment paper.

In a small bowl, mix shredded cheddar and Monterey Jack cheese. If desired, sprinkle in 1/2 tsp taco seasoning and toss to combine.

For each bowl, place about 1/2 cup of the mixed cheese in a flat circle on a piece of parchment paper in the air fryer basket (or baking sheet), leaving space between circles. You may need to do this in batches.

Air fry for 5-7 minutes, or bake for 8-10 minutes, until the cheese is melted, bubbly, and edges are golden brown and crispy.

Carefully remove the parchment paper with the melted cheese from the air fryer/oven. While still warm and pliable, immediately drape each cheese crisp over an inverted small bowl or ramekin to form a "bowl" shape. Let cool completely (about 10-15 minutes) to firm up. If they become too stiff to shape, briefly warm them again to soften.

While the cheese bowls are cooling, heat olive oil in a large skillet over medium-high heat. Add ground beef and any optional diced onion. Cook, breaking up the meat with a spatula, until browned and no longer pink, about 7-8 minutes.

Drain any excess grease from the skillet.

Stir in the taco seasoning and water. Bring to a simmer and cook for 2-3 minutes, stirring occasionally, until the liquid has mostly evaporated and the meat is well-coated. Remove from heat.

In a large mixing bowl, combine the chopped romaine lettuce, cherry tomatoes, red onion, black olives (if using), and diced avocado.

To assemble, place a cooled cheese bowl on each serving plate.

Fill each cheese bowl with a generous portion of the mixed salad greens.

Top the greens with a scoop of the warm taco meat.

Garnish each bowl with a dollop of sour cream, a spoonful of salsa, a sprinkle of fresh cilantro, and extra shredded cheddar cheese. Add sliced jalapeños and a lime wedge on the side, if desired.

Serve immediately and enjoy your delicious Keto Taco Salad Cheese Bowls!