Cook squash in boiling water to cover 7 minutes or until tender but still firm. Drain and cool slightly. Remove and discard stems. Cut each squash in half lengthwise; scoop out pulp, leaving a 1/4 inch shell. Reserve the squash pulp.
Saute garlic, onion, green pepper, and jalapeno in olive oil until crisp-tender. Sir in squash pulp, and cook, stirring often, until liquid has been absorbed. Add chili powder, salt and pepper; remove from heat. Add Monterey jack cheese and sour cream. Stir well.
Place squash shells in a lightly greased 12x8x2 inch baking dish. Spoon squash mixture evenly into shells. Bake at 350 degrees for 25 minutes. Divide picante sauce, Cheddar cheese and ripe olives evenly among the squash. Bake an additional 5 minutes.