Combine the cumin, pimenton, 1 of the garlic cloves, the rosemary, lemon zest, half of the lemon juice, the red pepper flakes, 1 teaspoon olive oil and a pinch salt in a small bowl. Gently massage the spice rub all over the bird, being careful not to tear the skin.
Coat a large saute pan with olive oil over medium-high heat. Sprinkle the poussin with salt, and place in the pan, skin-side down. Lay the foil-wrapped brick on top of the bird to press it into the pan. Cook the poussin until the skin is a lovely dark golden brown, about 7 minutes. Flip the bird and continue to cook, without the brick, until the internal temperature has reached at least 150 degrees F, 5 to 7 minutes more.
Transfer the poussin to a parchment paper-lined sheet tray and continue to cook in the oven until the internal temperature of the thickest part of the meat reaches 165 degrees F.
Meanwhile, remove the excess fat from the saute pan and pour in the white wine, remaining lemon juice and garlic. Scrap up any brown bits stuck to the bottom of the pan and cook over high heat until the wine has reduced by more than half. Add the chicken stock and simmer until slightly thickened. Taste and adjust the seasoning.
Arrange the poussin on a plate, and spoon the juices on top.