Add ½ teaspoon butter (or oil) to a large saucepan. Add onion and fresh garlic (if using), saute over medium heat until soft.
Add the chopped spinach to the pan and cover, turning the heat to medium-low. Stir occasionally until the spinach has wilted. Remove from heat.
Place the stuffing mix in a large bowl. Add remaining ingredients along with the wilted spinach and stir well to combine.
Gently press the stuffing mixture into an 8x8 inch pan.
Bake for 30 minutes, or until the top is golden brown and a knife inserted in the middle comes out clean.
Notes
The flavors in this casserole are even better on day two, so why not prepare a day ahead and reheat!
Refrigerate leftovers, covered for up to 4 days. Portions can be frozen wrapped in plastic wrap and set in zippered bags for up to 3 months. Perfect for an easy grab and go lunch option.
Reheat thawed casserole in the microwave, or covered with foil in the oven.