Preheat oven to 450°F

Pulse carrots and celery in food processor until finely chopped

Heat 1 tablespoon olive oil in large nonstick skillet over medium high heat. Add chopped veggies and cook, stirring frequently until golden and soft.

Add ground beef and 4 teaspoons of tomato paste and cook until browned

Add 1/2 cup water, raisins, 1 tablespoon vinegar and 3/4 teaspoon kosher salt. Bring to simmer and cook until most of the water is absorbed. Let cool slightly

Toss peppers (halved lengthwise and seeded) in 1/2 tablespoon olive oil in microwave safe bowl. Cover in plastic wrap and microwave until pliable (8-10 mins).

Stir couscous in to beef mixture.

Whisk together 2 tablespoons tomato paste, 1 tablespoon vinegar, and 3/4 cup water in bottom of large baking dish.

Carefully transfer peppers to dish cut side up and fill with mixture. Sprinkle with cheese. Cover with foil and bake until peppers are tender and stuffing is hot. 20-25 mins. Drizzle with tomato cooking liquid.