Gluten-Free Taco Quesadillas

2 tablespoons olive oil
1 small onion, minced
1 clove garlic, minced
1 pound ground sirloin
2 teaspoons cumin
2 teaspoons chili powder
1 teaspoon salt
1 teaspoon cracked black pepper
4 soft corn tortillas
1 cup shredded cheddar cheese
1/2 head iceberg lettuce
2 large plum tomatoes, finely diced (1 cup)
Whole-milk sour cream, for garnish
Chopped cilantro leaves, for garnish

Place oil in a skillet over medium-high heat. Add onions and garlic. Reduce heat to medium and saut