Captain's Chicken Filled Taco Shells

Preheat oven to 375 F [190 C]. Peel and chop onion; wash, seed, remove membranes and chop green pepper; reserve. Arrange frozen vegetables in a glass, microwave-safe dish; cover with plastic wrap and punch holes. Pour in water and microwave for 2 to 3 minutes, at 'MAXIMUM'; reserve. Cut chicken into 1/3-inch [8 mm] cubes. In an enamel cast iron frypan, heat olive oil; brown chicken cubes for 3 minutes on each side. Add reserved chopped onion and green pepper; brown for 3 minutes. Mix in sauce and reserved vegetables; simmer for 5 minutes, uncovered. Meanwhile, heat taco shells in preheated oven for 5 minutes. Fill taco shells with vegetable/chicken mixture. Sprinkle with grated cheese. Serve hot.