In a medium bowl, combine the chicken cubes, 1/2 cup Greek yogurt, 2 minced garlic cloves, 1 tbsp grated ginger, 1 tsp garam masala, turmeric, cumin, cayenne, and salt. Mix well to coat. Cover and refrigerate for at least 30 minutes or up to 8 hours.

Heat 2 tsp of avocado oil in a large skillet over medium-high heat. Add the chicken in a single layer (work in batches if needed) and cook for 3-4 minutes per side, until golden brown and cooked through. Remove from the skillet and set aside.

In the same skillet, add the remaining 1 tsp of oil. Add the chopped onion and cook for 4-5 minutes until soft. Stir in the 3 cloves of minced garlic and 1 tbsp of grated ginger, and cook for 1 minute until fragrant.

Add the 1.5 tsp garam masala, paprika, and ground coriander to the skillet. Stir constantly for 30 seconds until aromatic.

Pour in the crushed tomatoes, scraping any browned bits off the bottom of the pan. Bring to a simmer and cook for 10 minutes, allowing the sauce to thicken.

Reduce heat to low and stir in the remaining 1/2 cup of Greek yogurt until the sauce is smooth and creamy. Return the cooked chicken to the skillet and stir to coat. Let it warm through for 1-2 minutes. Garnish with fresh cilantro and serve immediately.