Position racks in the upper and lower thirds of the oven; preheat to 450 degrees F. Halve the pork tenderloin crosswise, then halve lengthwise. Rub two-thirds of the garlic into the meat along with 1 teaspoon each oregano and cumin and a generous pinch each of salt and pepper. Set aside 10 minutes.
Toss the sweet potato and broccoli in a large bowl with 1 tablespoon olive oil, the remaining 1/4 teaspoon cumin, 1/2 teaspoon salt and a few grinds of pepper. Spread in a single layer on a baking sheet and roast on the upper oven rack, stirring once, until lightly browned and tender, about 25 minutes. Meanwhile, cook the quinoa as the label directs.
While the vegetables and quinoa cook, heat 1 tablespoon olive oil in a large ovenproof skillet over medium-high heat. Add the pork and cook until browned, about 5 minutes. Flip the pork and transfer the skillet to the lower oven rack. Roast until a thermometer inserted into the center registers 140 degrees F to 145 degrees F, about 5 minutes. Transfer to a cutting board.
Stir the orange juice, vinegar, red pepper flakes, remaining garlic, 1 tablespoon olive oil and 1/4 teaspoon oregano in a small bowl; season with salt and pepper. Divide the quinoa and vegetables among bowls. Slice the pork and add to the bowls. Drizzle with the orange sauce.