Wash the mixed salad greens in cold water, spin dry in a salad spinner or pat dry with clean kitchen towels, and transfer to a large salad bowl. Tear any large leaves into bite-sized pieces.

Prepare tomatoes

Core and quarter the tomatoes (or cut into 6–8 wedges if large). If using cherry tomatoes, halve them. Add tomato pieces to the bowl with the greens.

Prepare red onion

Peel the red onion, slice it very thin (use a sharp knife or mandoline). If the onion flavor is strong, place the slices in cold water for 5 minutes, then drain and pat dry. Add the slices to the salad bowl.

Cheese and add-ins

Sprinkle the shredded or crumbled cheese evenly over the salad. Add the croutons last so they remain crisp.

Dressing

Make vinaigrette

In a small jar or bowl, combine the red wine vinegar, Dijon mustard, honey, salt, and pepper. Whisk or shake to combine, then slowly stream in the olive oil while whisking until the dressing is emulsified and slightly thickened. Taste and adjust seasoning with additional salt, pepper, or a bit more honey if too sharp.

Dress the salad

Just before serving, drizzle about 2 tablespoons of the vinaigrette over the salad (reserve any extra for guests to add). Toss gently but thoroughly so the greens, tomatoes, onion, cheese, and croutons are evenly coated. Add more dressing to taste, being careful not to overdress. Serve immediately.