Heat Grapeseed Oil (2 teaspoon) in a large skillet over medium heat until hot and shimmering but not smoking, about 2 minutes.
Add Onion (1) and cook, stirring occasionally, until softened, about 4 minutes.
Add Garlic (3 clove), Chili Powder (2 tablespoon), Ground Cumin (1 teaspoon), and Salt (1/2 teaspoon); cook, stirring constantly, until fragrant, about 1 minute.
Add Chicken Thigh (1 pound) and cook, stirring occasionally, until it is no longer pink, about 5 minutes.
Add Canned Crushed Tomatoes (1/2 cup), Water (1/2 cup), Granulated Sugar (1 teaspoon) and Apple Cider Vinegar (2 teaspoon); bring to simmer.
Reduce heat to medium-low and simmer, uncovered, stirring frequently, until liquid has reduced and thickened, about 10 minutes. Taste, and adjust seasonings with Kosher Salt and Freshly Ground Black Pepper (to taste).
Wrap Tortilla (as needed) in foil, and place in a 350 degrees F (180 degrees C) oven for 15 minutes or until warm.
Remove from oven, and transfer to tea towel to keep warm. Place chicken, Shredded Cheddar Cheese (to taste), Romaine Lettuce (to taste), Salsa (to taste), Sour Cream (to taste), and Avocado (to taste) in bowls. Assemble as desired.