Preheat oven to 450. Arrange zucchini cut side up in 9x13 baking dish. Add 1/2c water to dish,cover with foil and bake till zucchini begins to soften,about 15 mins.
Meanwhile,in a med. skillet,heat olive oil ocer med-high heat. Add onion and cook until softened,about 3 mins. Add the beef and cumin and cook,breaking meat up,until just browned,about 4 mins;season with salt and pepper. Stir in tomatoes and pickled jalapenos.
Uncover the baking dish,pour off water and season the zucchini wit salt. Fill with the beef mixture and sprinkle cheese on top. Bake,uncovered until the cheese is melted,about 10 mins.