Add the chicken chunks, 1 cup of coconut milk and 1 tsp garam masala to a plastic bag or bowl and mix well. Marinate for 20 minutes (or up to 24 hours).
Cook the rice/grain according to the package and set aside.
Add 1 TBSP oil or butter to a skillet over medium heat. Add the chicken and cook for 5-7 minutes on each side, until it's fully cooked through.
Add the chopped onion, carrots, garlic and ginger to the pan with a splash of water to get some of the residue from the chicken off the bottom of the pan. Add the garam masala, cumin and nutmeg to the pan with salt and pepper to taste. Stir frequently for 5-7 minutes, until the onions are translucent and fragrant.
Add the whole can of tomato sauce to the pan, stir and bring the sauce to a low boil. Then simmer and cook uncovered for about 10-15 minutes. If your sauce thickens too much, add 1-2 TBSP water to thin it out.
After 10 minutes turn off the heat, pour in the remaining coconut milk/whole milk/yogurt and stir. Taste the sauce and adjust spices as necessary. I added more salt and garam masala at this point.
Assemble: Divide the cooked rice between your 3 meal prep containers. Then divide the tikka masala between the three containers. Top with cilantro and lime wedges if desired.