Toss any lettuce or field greens you have on hand with this easy dressing of olive oil, vinegar, and Dijon mustard.
Combine minced onion and vinegar in a small bowl; let stand 5 minutes. Add oil, salt, pepper, and mustard; stir well with a whisk.
Place the lettuce, sliced onion, and tomatoes in a large bowl; toss gently to combine. Drizzle vinaigrette over salad; toss gently to coat.
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