In a shallow pan, mix the lemon juice, olive oil, garlic, 1/2 salt, chipotle powder. Set aside a tablespoon for the vegetables. Add fish, turning once and marinate for 20 minutes. While the fish is marinating, slice the avocado, onions and zucchini lengthwise.
Mix the sour cream wit the chives, season with 1/2 tsp salt and pepper and set aside. Grill the fish on the BBQ (alternatively you can pan fry the as well) 5 to 6 minutes per side- grilling the onion and zucchini for the last 2 minutes, and hamburger buns as well.
Spread D’Italiano buns with a tablespoon per side of the sour cream mixture, and top with grilled zucchini, onions and avocado slices.