Season boneless, skinless chicken thighs with salt, pepper, and lemon pepper. Heat olive oil in the base of a soup pot on high heat, then place the chicken in the pot. Cook the chicken thighs on both sides until the chicken is cooked through (you can use the pot lid to help the cooking process).
Leave any reserved liquid in the pot, but transfer the chicken thighs aside for later. Add your frozen medley of peas, carrots, and corn to the pot and heat the veggies on high heat to thaw and cook in the leftover juices. Season them with salt, pepper, onion powder, and minced garlic.
Once the veggies are tender and fragrant, pour chicken broth and almond milk into the pot. Bring the pot to a boil, then reduce the heat to a simmer. Chop the chicken thighs into tiny pieces and return the chicken to the soup.
Stir nutritional yeast into the soup, then let the soup simmer to reduce. Once the broth looks like a thickened, pale yellow cream, the soup is done. Taste and adjust your seasoning to your liking, and serve hot.