Make the muffin tin meatloaf: Preheat the oven to 400°F (205°C) and spray a 12-cup muffin tin generously with cooking spray.
In a large bowl, mash together the beans, oil, tamari, tomato paste, ground flax seeds, and 2 tablespoons water. Add the walnuts, dried onion, garlic powder, celery seeds, thyme, paprika, pepper, and salt, then add ½ cup (28 g) panko to create a firm, moist mixture. If it seems too wet, work in more breadcrumbs a tablespoon at a time. Divide the mixture into the oiled muffin cups, and firmly press the mixture into the cups.
Make the gastrique: Combine the ketchup and vinegar in a small bowl and spread over the tops. Bake for 15 to 18 minutes, until the loaves are firm and the topping has browned on the edges.
Make the sautéed spinach: Make the spinach as close to serving time as possible, since spinach loves to wilt. Preheat a large skillet over medium heat. Mince the garlic cloves. Sauté them in the oil for about 1 minute. Add the spinach and salt and use tongs to flip it around in the pan so it begins to wilt. Turn the heat off before all the spinach has wilted and continue to toss in the pan until fully wilted.
The muffin tin will be very hot when you remove it from the oven, so use oven mitts or kitchen towels. Use a butter knife or an offset spatula to help loosen and remove the loaves from the edges. Serve two or three veggie loaves with a side of mashed potatoes and spinach!
Make the mashed potatoes: Place the potatoes in a large pot and add enough cold water to cover them. Bring to a boil over high heat, then reduce the heat to medium-low and simmer for about 10 minutes, until fork-tender. Drain the potatoes and return them to the pot. Add the vegan butter, salt, and pepper and mash with a potato masher. Taste for salt and pepper!