Whisk together the milk and lemon juice in a large flat-bottom glass container. Let it set for 5 minutes to curdle.
Add the chicken thighs into the milk. Cover with an airtight lid and allow the thighs to marinate for at least 4 hours or overnight.
In a shallow bowl, whisk together the flour, onion powder, garlic powder, salt, paprika, and oregano. (Or simply use my homemade low-FODMAP spice mixture -- see notes)
Pour oil into a deep saucepan, filling to at least 2-3 inches of oil. Heat the oil on the stovetop until it reaches 350°F.
Using tongs, take each chicken thigh from the milk mixture and dredge through the flour mixture. Thoroughly coat each chicken thigh with the flour mixture.
Transfer 2-3 thighs into the hot oil at a time, taking care not to overcrowd your saucepan. The temperature of the oil will go down when the chicken is added, but try to maintain as close to 350°F as possible throughout the process.
Allow the chicken to fry on each side for 6-7 minutes, flipping with tongs so both sides get equal time in the hot oil. The internal temperature of the chicken should be 165°F. Be careful of hot oil splatters!
Remove the fried chicken from the pan and onto a cooling rack or a plate lined with paper towels. Repeat with the remaining coated chicken thighs.
Serve fresh and warm for optimum crunchiness. Store leftovers in an airtight container in the fridge and re-heat in an air fryer or oven, not microwave.