This is a fabulous combination. I had this cut out of a magazine to try one day, stuck into a binder. I'm not sure what magazine it came from. It's not mine....just not sure who it belongs to! Cooking time is standing time to pickle the onions.
Combine 1/4 cup water, 2 tablespoons vinegar, and 1 tablespoon agave in a small bowl. Add onion; toss to coat. Marinate at room temperature for 30 minutes; drain.
Combine remaining 2 tablespoons vinegar, remaining 1 teaspoon agave, mustard, pepper, and salt in a large bowl, stirring with a whisk. Gradually add oil, stirring constantly with a whisk. Add salad greens; toss gently to coat.
Arrange about 1 cup salad on each of 8 plates. Top each serving with about 1 tablespoon onion, 1 tablespoon cheese, and about 6 raspberries.