Peel and finely mince the ginger and garlic. Dice the half onion into small pieces.
Toss the cubed chicken breast with 1 tablespoon of garam masala and a pinch of salt.
Heat 1 tablespoon of olive oil in a skillet over medium-high heat. Add the chicken in an even layer and sear until golden brown on all sides, about 4-5 minutes. Remove the chicken and set aside.
In the same pan, add the remaining tablespoon of olive oil. Add the diced onion, ginger, and garlic and sauté until translucent and fragrant, about 3-4 minutes.
Stir in the tomato paste, paprika, cayenne pepper, remaining garam masala, and a pinch of salt. Cook for another 1-2 minutes to deepen the flavors.
Pour in the crushed tomatoes, stir to combine, and bring to a gentle simmer. Cook uncovered for 10 minutes to thicken the sauce and meld flavors.
Add the seared chicken back into the pan. Cover and simmer for 7-10 minutes, or until the chicken is cooked through and tender.
Remove the pan from heat. Stir in the Greek yogurt and fresh lemon juice gently until creamy and well blended. Adjust salt and cayenne to taste.
Sprinkle chopped cilantro leaves on top for garnish. Serve hot with basmati rice or warm naan bread.