Rinse whole lettuce leaves and pat dry, being careful not to tear them. Set aside.
Heat a skillet over medium-high heat. Add olive oil to the hot skillet, then add ground beef. Stir and cook until browned - about 5-7 minutes.
Drain and discard grease. Transfer ground beef to a bowl. In the same skillet, stir and cook the onion and zucchini until slightly tender - about 5-10 minutes.
Stir hoisin sauce, garlic, soy sauce, vinegar, ginger, and chili pepper sauce into onion-zucchini mixture. Add water chestnuts, green onions, and cooked ground beef to this mixture.
Stir and cook until the onions just begin to wilt, about 2 minutes.
Arrange the four lettuce leaves around the outer edge of a large serving platter and place one fourth of the ground beef mixture in the center of each leaf. Enjoy!