Combine the garlic powder, pimenton, rosemary and lemon zest in a small bowl. Toast the coriander and cumin seeds in a small pan until fragrant, about 5 minutes. Combine the toasted seeds with the other spices and grind in a spice grinder.
Season the game hen with salt and crushed red pepper.
Heat the olive oil in a cast-iron skillet over high heat. Sear the hen, skin-side down, adjusting the heat as necessary. Place the brick on top of the hen and cook until evenly browned. Remove the brick and flip the hen. Rub some of the spice mixture onto the skin side. Flip the hen over and rub some of the spice mixture onto the back side. Roast in the oven, skin-side down, for 15 minutes. Flip the hen skin-side up and continue to roast until the skin is crispy and the internal temperature is 165 degrees F, about 15 minutes more. Let rest.
Serve drizzled with olive oil, with Mashed Potatoes on the side.
Place the potatoes and garlic in a large pot and cover with cold water. Bring to a boil over medium-high heat and heavily season the cooking water with salt. Turn down the heat and simmer until the potatoes are fork tender; drain. Pass the potatoes through a food mill into a bowl.
Meanwhile, bring the cream to a simmer in a small saucepan. Add 1/4 cup of the heated cream and the cold butter to the potatoes and stir vigorously. Add more cream and butter as needed. Season with salt.