Wash and dry produce.

Dice tomato into ½-inch pieces. Halve, peel, and thinly slice shallot. Trim and halve cucumber lengthwise; slice crosswise into ¼-inch-thick half-moons. Trim and discard root end from lettuce; chop leaves into bite-size pieces.

In a medium bowl, whisk together vinegar, mustard, Greek vinaigrette, ¼ tsp Tuscan Heat Spice, 2 TBSP olive oil, and 1 tsp sugar (½ tsp Tuscan Heat Spice, 4 TBSP olive oil, and 2 tsp sugar for 4 servings). Season with salt and pepper.

Add tomato and as much shallot as you like to bowl with dressing; toss to combine. Set aside to marinate.

Heat a drizzle of oil in a large pan over medium-high heat. Add chicken and cook until browned and cooked through, 5-7 minutes per side.

Transfer to a cutting board.

Dice chicken into 1-inch pieces.

Add chicken, cucumber, and lettuce to bowl with tomato and shallot. Toss to combine.

Divide salad between plates. Drizzle with remaining dressing from bowl. Top with feta and serve.