Heat avocado oil in a large skillet over medium heat. Add shrimp ; sprinkle with salt and pepper. Sauté for 2 minutes. Add garlic and cook, tossing, until shrimp are opaque and light pink and no gray tone remains, 1 to 3 minutes. Transfer shrimp mixture to a medium bowl.
Whisk lemon zest, lemon juice, mustard, and honey in a large bowl. Add olive oil in a slow, steady stream, whisking constantly. Whisk in ½ teaspoon salt and ¼ teaspoon pepper. Fold tomatoes, cucumber, and herbs into dressing, then fold in avocado and shrimp.
Divide lettuce among 4 plates. Spoon shrimp mixture evenly over lettuce. Sprinkle with pepper.