For the tomatillos: Preheat the broiler and set the tomatillos, garlic, jalapeños and onions out on a foil-lined tray. Drizzle the ingredients with a little olive oil and sprinkle with salt and pepper. Place the vegetables under the broiler 3 to 4 inches from the top and cook until the tomatillos and onions are well charred, 5-6 minutes. Turn the vegetables and broil until charred all over, 4-5 minutes longer. Remove from the oven and transfer to a blender with the chicken stock, cilantro and lime juice. Purée until completely smooth. Place in a large sauté pan over medium-low heat and warm through. Season with salt and pepper.
For the turkey enchiladas: Set a large sauté pan over medium-high heat and coat with the oil. Add the turkey and garlic, and brown well, 3-4 minutes. Add the cumin, coriander, paprika, oregano and onions, and cook until well-browned, 10 minutes longer. Season with salt and pepper. Transfer to a platter and let cool.
Preheat the oven to 375°F and grease a 9x13” gratin dish with oil.
Spoon some of the tomatillo sauce into the bottom of the pan to lightly coat it. Dip each tortilla into the heated tomatillo sauce (this will both flavor the tortilla and also make it more pliable). Spoon 1/4 cup of the ground turkey filling onto each tortilla. Divide 1/2 cup of the shredded Jack cheese between each tortilla. Fold the tortillas over the filling and place them seam-side down in the gratin dish. Place 6 enchiladas in the pan and top with more tomatillo sauce so they are just barely covered. Top with remaining 1/2 cup of Jack cheese and sprinkle with crumbled queso fresco. Place on a tray (to catch any drips) and bake until the cheese has melted and the sauce is bubbling, 15 to 17 minutes. Finish under the broiler to brown further if desired. Remove from the oven, let cool slightly and garnish with the chopped cilantro. Serve with the sour cream on the side.