MAKE THE LEMON VINAIGRETTE: In a small bowl or measuring cup, whisk together the lemon juice, lemon zest, garlic, mustard, salt, and pepper. Let rest a few minutes. Slowly whisk in the olive oil until well-combined or emulsified. Set aside.
COOK THE ORZO AND ASPARAGUS: In a 6 or 8-qt covered pot, bring 4-5 quarts cold water to boil. Add a generous teaspoon of kosher salt. Pour in orzo and cook for 6-7 minutes, stirring occasionally. Add the chopped asparagus and cook another 2-3 minutes or until everything is just barely tender. Drain, and while hot, drizzle with about a tablespoon of olive oil. Sprinkle with a good pinch each salt and pepper. Stir. (You can do this in the colander or in a large mixing bowl. If you've done it in the colander and let the cooking pot cool for a few minutes, you can use the cooking pot as the mixing bowl and save even more dishwashing.)
IN A LARGE BOWL, STIR TOGETHER the orzo and asparagus with the tuna, vegetables (except the tomatoes and avocado), and olives.
POUR THE VINAIGRETTE OVER THE SALAD and mix gently. Taste and adjust seasonings.
DIVIDE THE SALAD BETWEEN 4 BOWLS lined with greens, if using, and garnish with tomatoes and avocado. Grind a little black pepper over everything. Serve each with a lemon wedge. Store leftovers well-covered in the refrigerator for 2-3 days.