Preheat oven to 375°F. Toss potatoes with 1 tablespoon oil in medium bowl. Place on 13x9-inch rimmed baking sheet or roasting pan. Sprinkle with salt. Roast 20 minutes.

Meanwhile, heat 2 tablespoons oil in medium skillet over medium heat. Add mushrooms and onion; sauté until mushrooms are beginning to brown and onion is translucent, about 4 minutes. Remove from heat; mix in sage and thyme. Cool slightly.

Mix buffalo, mushroom mixture, egg, 1/2 cup tomato sauce, panko, salt, and pepper in large bowl. Push potatoes to sides of baking sheet; shape buffalo mixture into 6x3-inch loaf in center of sheet. Roast 30 minutes. Combine 1/4 cup tomato sauce and red pepper in small bowl. Pour over top of meatloaf. Roast 20 minutes longer. Remove from oven; let rest while preparing spinach.

Heat remaining 2 tablespoons oil and garlic in large pot over medium-high heat. Add spinach, and toss until wilted, about 3 minutes. Season to taste with salt. Slice meatloaf; serve potatoes and spinach alongside.

*Available in the Asian foods section of some supermarkets and at Asian markets.