01 - Preheat a skillet over medium-high heat. Rub the chicken breasts with olive oil, salt, and pepper on all sides.
02 - Place the chicken in the skillet and cook for 5–7 minutes per side until golden brown and fully cooked. Transfer to a plate and rest for 5 minutes. Slice thinly across the grain.
03 - In a small bowl, stir together the basil pesto and mayonnaise or Greek yogurt, if using, until smooth.
04 - Heat the tortillas briefly in a dry skillet or microwave for a few seconds each until warm and pliable.
05 - Spread about 1 tablespoon of the pesto mixture over each tortilla. Layer with baby spinach, sliced chicken, avocado, cherry tomatoes, and red onion.
06 - Fold in the sides of each tortilla and roll up tightly. Slice each wrap in half and serve immediately.