In a large cast-iron or other heavy skillet, heat 2 tablespoons butter over medium heat. Add shallot and garlic; cook 1-2 minutes. Remove from heat; stir in tequila, lime zest and lime juice. Cook over medium heat until liquid is almost evaporated, 2-3 minutes., Add olive oil and remaining butter; stir in shrimp and zucchini. Sprinkle with salt and pepper. Cook and stir until shrimp begin to turn pink and zucchini is crisp-tender, 4-5 minutes. Sprinkle with parsley and additional lime zest.