Cut chicken in half horizontally. Combine chicken, yogurt, and 1/2 teaspoon garam masala. Place on a foil-lined baking sheet coated with cooking spray; sprinkle with 1/8 teaspoon salt. Broil 5 minutes on each side.
Heat a skillet over medium-high heat. Place tomatoes in a mini chopper; pulse until almost smooth. Add oil to pan. Add 1 1/2 teaspoons garam masala, ginger, red pepper, and garlic; cook 1 minute. Stir in tomatoes; simmer 4 minutes. Stir in 1/2 teaspoon salt and cream; cook 1 minute. Cut chicken into pieces. Add chicken to pan; toss.
Place pitas on baking sheet. Broil 1 minute each side. Spoon 1/2 cup chicken onto each. Top with onion and cheese. Broil 2 minutes. Sprinkle with cilantro.