Whisk 1/2 cup olive oil, red wine vinegar, lemon juice, minced garlic, 2 tablespoons oregano, and ground cumin in medium bowl; season to taste with salt and pepper. Transfer 1/2 cup of dressing to large bowl; add lamb chops and stir to coat. Let marinate 30 minutes, stirring occasionally. Add grape tomatoes to remaining dressing in medium bowl; toss to coat.