1. Place beef in freezer.
2. Combine water, juice, and sugar in a bowl. Add jalapeños; toss well.
3. Heat a large, heavy skillet over high heat. Cut beef across grain into thin slices. Add 1 tablespoon oil and beef to pan; sprinkle with 1/4 teaspoon salt and 1/4 teaspoon black pepper. Sauté 3 minutes or until done; remove from pan. Add sliced mushrooms, zucchini, 1/4 teaspoon salt, and 1/4 teaspoon black pepper to pan; sauté 4 minutes. Remove from pan. Add 1 tablespoon oil to pan. Add onion, red pepper, garlic, chili powder, 1/4 teaspoon salt, and 1/4 teaspoon black pepper; sauté 5 minutes or until crisp-tender. Add beef and mushroom mixture; cook 2 minutes or until heated.
4. Heat corn tortillas according to directions. Place 3 tortillas on each of 4 plates, and top each with 1/3 cup beef mixture. Top evenly with jalapeños and cilantro.