Wash and dry the spring mix thoroughly (use a salad spinner or pat dry). Halve or quarter the heirloom tomatoes depending on size to yield about 1 cup; place in a bowl. Thinly slice the red onion into half-moons and soak in cold water for 5 minutes if you want milder onion, then drain and pat dry. Combine spring mix, tomatoes and onion in a large serving bowl. Add chopped parsley if using; toss gently and set aside.

Hamburger patties

Form patties

Place the ground beef in a bowl. Sprinkle kosher salt, black pepper and garlic powder over the meat. Gently mix until just combined—do not overwork. Divide into two 4 oz patties (or one large patty, depending on preference) and press a slight indent in the center of each to promote even cooking.

Cook patties

Heat a skillet or cast-iron pan over medium-high heat and add 1 tablespoon olive oil. When the oil is shimmering, add the patties. Cook undisturbed for about 3-4 minutes until a crust forms. Flip and cook 3-4 minutes more for medium; adjust time for desired doneness (longer for well-done, shorter for rare). Internal temperature targets: 160°F (71°C) for well-done. Remove patties to a plate and let rest 3 minutes, then slice or break into large pieces suitable for topping the salad.

Balsamic vinaigrette

Make vinaigrette

In a small bowl or jar, combine 1 tablespoon balsamic vinegar, 3 tablespoons extra-virgin olive oil, 1/2 teaspoon Dijon mustard, 1/2 teaspoon lemon juice (or a splash of water), 1/4 teaspoon salt and 1/4 teaspoon black pepper. Whisk or shake until emulsified. Taste and adjust seasoning. Use about 1–2 tablespoons per serving, or drizzle to preference.

Ranch dressing (alternative)

Make ranch

In a small bowl, whisk together 3 tablespoons mayonnaise, 2 tablespoons sour cream and 1 tablespoon buttermilk or heavy cream until smooth. Stir in 1 teaspoon fresh dill, 1 teaspoon fresh chives, 1/4 teaspoon garlic powder, 1/4 teaspoon onion powder, 1/4 teaspoon salt and 1/4 teaspoon black pepper. Thin with an extra splash of cream if needed to reach desired consistency. Refrigerate if not using immediately.

Assembly

Dress salad

If using vinaigrette, add 1–2 tablespoons to the salad base and toss gently to coat the greens, tomatoes and onion. If using ranch, lightly dress the salad with 1–2 tablespoons or serve on the side.

Top with patties & serve

Top the dressed salad with the sliced or crumbled hamburger patties, distributing evenly. Garnish with additional chopped parsley if desired. Serve immediately while patties are still warm.