Season the lamb roasts generously with salt and pepper, wrap in plastic and refrigerate overnight. Bring the roasts to room temperature before cooking.
Preheat the oven to 325°. In a food processor, pulse the almonds with the garlic until finely chopped. Add the mint leaves, cheese and 3/4 cup of the oil and process until smooth. Season the pesto with salt.
In a large skillet, heat the remaining 2 tablespoons of olive oil until shimmering. Add the roasts and cook over high heat, turning, until browned all over, about 10 minutes. Transfer the roasts to a large roasting pan and spread half of the pesto over them. Cover tightly with foil and roast for about 2 hours, until an instant-read thermometer inserted in the center of each roast registers 170°. Remove the foil, increase the oven temperature to 425° and roast for 30 minutes longer, until browned on top. Transfer the lamb to a cutting board and let rest for 10 minutes.
Remove the strings and carve each roast into 1/2-inch-thick slices. Serve with the remaining pesto and lemon wedges.