To a large skillet over medium high heat, add the olive oil and beef. Cook until browned, then add in the onion, garlic and bell peppers. Saute for another 5-6 minutes, then add in the cabbage, tomatoes, tomato paste, and mustard. Toss until coated and allow the cabbage to slightly wilt, about 5-6 minutes.
Sprinkle the bottom of a 13x9 " baking dish with cornstarch. Using a slotted spoon, transfer the mixture to the baking dish, leaving the liquid behind. Fill the pan half way up, then add half of the cheese and pickles, then finish with the remaining cabbage mixture, cheese and pickles.
Bake for 17-20 minutes until the cheese melts and browns and the mixture is heated through.