Preheat the oven to 450 degrees F. Line a rimmed baking sheet with foil. Toss the cauliflower and red onion with 1 tablespoon olive oil in a large bowl; arrange on one side of the prepared pan. Toss the chicken with the remaining 1 tablespoon olive oil, the coriander, paprika, grated garlic and half of the lemon zest in the same bowl; arrange skin-side up on the other side of the pan. Season the vegetables and chicken with salt and pepper. Roast until the vegetables are browned and the chicken is crisp and cooked through, about 30 minutes.
About 10 minutes before the chicken is done, combine the peas, 1/4 cup water and the sliced garlic in a medium microwave-safe bowl; cover with plastic wrap and poke a small hole in the plastic. Microwave until the peas are warmed through, about 5 minutes. Transfer to a food processor and add the butter, mint and the remaining lemon zest; puree, adding more water if needed to loosen. Season with salt and pepper.
Serve the chicken with the roasted vegetables, pea puree and lemon wedges.