Pan Grilled Portabella Fajitas

1 pound fresh white mushrooms, cut in 1/4-inch thick slices
8 ounces portabella caps, halved and cut in 1/4-inch slices
1/2 teaspoon salt
1 teaspoon finely chopped garlic
2 tablespoons vegetable oil
1 large onion, cut into 8 wedges
1 large red bell pepper, cut into 1/2-wide strips
2 teaspoons finely chopped fresh jalape