In a bowl, combine the chicken cubes, yogurt, ginger-garlic paste, lemon juice, garam masala, turmeric powder, cumin powder, coriander powder, red chili powder, and salt. Mix everything well so the chicken is evenly coated. Cover the bowl and let it marinate in the fridge for at least 30 minutes.
Heat the butter in a large skillet or pan over medium-high heat. Once the butter is melted and hot, add the marinated chicken.
Cook the chicken, stirring occasionally, until it's cooked through and slightly browned on all sides. This should take about 8-10 minutes. The chicken should be juicy and tender.
Carefully slice each croissant horizontally, almost all the way through, but leaving a "hinge" on one side. This will create a pocket for the filling.
Once the chicken is cooked, let it cool slightly. Then, carefully spoon the chicken tikka filling into each croissant. Don't overfill them, or they'll be hard to close.
Serve the chicken tikka croissants immediately. If you like, you can garnish them with fresh cilantro and thinly sliced red onion.