Press out the moisture in the tofu using a tofu press or by placing it between two towels and placing something heavy on top. Let rest for 15 minutes.
Meanwhile heat the oil over medium heat in a skillet. Add the garlic, onions, spinach, and mushrooms. Cook until softened. Squeeze out any excess moisture. Season with salt, pepper, dried herbs, and red pepper flakes.
Add the tofu, lemon zest, lemon juice, and vinegar to a food processor and pulse until completely smooth.
Remove and fold in vegetables and nutritional yeast. Taste and adjust seasoning if needed.
Pour into slow cooker and cook for 4 hours on low until set.