In a mixing bowl, combine Greek yogurt, lemon juice, ginger-garlic paste, turmeric powder, garam masala, ground cumin, coriander, smoked paprika, chili powder, and salt. Add the chicken, ensuring it's coated evenly. Cover and refrigerate for at least 1 hour, or overnight for the best flavor absorption and tenderness.

Preheat your grill pan over medium-high heat or set your broiler to high. Remove the marinated chicken from the fridge, allowing it to sit for 10 minutes. Grill or broil the chicken for 4-5 minutes on each side until charred and cooked through, reaching an internal temperature of 165°F. Once done, set aside to rest.

In a large skillet, melt butter or ghee over medium heat. Add finely chopped onions and sauté for about 8-10 minutes until they're golden brown and soft. Stir in the garlic and ginger, cooking for an additional minute until fragrant before adding the turmeric, garam masala, cumin, and coriander spices.

Incorporate the tomato paste and crushed tomatoes into the skillet, stirring well to combine. Allow the mixture to simmer gently for about 10 minutes, reducing slightly and thickening.

Add the grilled chicken pieces to the simmering sauce, ensuring each piece is well coated. Let it cook for another 5 minutes, allowing the chicken to absorb the sauce’s flavors.

Stir in heavy cream or coconut milk for added creaminess, letting it heat through for a couple of minutes. Finish with a squeeze of fresh lemon juice to brighten the flavors.

Serve your sumptuous Gordon Ramsay Chicken Tikka Masala hot, draped over fluffy basmati rice or paired with warm naan or roti.