Heat a saute pan to medium heat (any size will do) and add avocado oil. When oil moves quickly around the pan, add onion and shallot. Cook, stirring, until both are softened and translucent, approximately 5-6 minutes. You can add splashes of water as necessary to prevent sticking/burning. Turn heat to low and add garlic. Cook, stirring constantly, until garlic is softened and fragrant, approximately 30 seconds. Turn off heat and set pan aside.
In a crockpot, combine all ingredients except corn and starch in the order listed. Stir to combine evenly, then stir in onion mixture. Cover with lid and cook on low heat for 7 hours or high heat for 4 1/2 hours. Add corn and cook another 1 hour on low or 1/2 hour on high.
In a small bowl, combine starch and 2 tablespoons water. Add slurry to chowder and stir until you notice the texture thicken, approximately 30 seconds. At this point, feel free to taste for more salt or even Sriracha and add accordingly. Serve immediately. Soup will keep in the refrigerator for 5 days, if the chicken was fresh upon use.