In a blender, combine all masala paste ingredients and blend until smooth. Set aside.
Cut baby eggplants lengthwise into quarters, stopping 1/4 inch from the stem to keep them intact. Gently separate the slits while holding the stem.
Carefully slather the masala paste into the slits of each eggplant in a thin layer, taking care not to break them apart. Set aside.
Heat 2 tablespoons oil in a large pan over medium heat. Add diced onions, a pinch of salt, and any remaining masala paste. Sauté until onions turn translucent, about 4-5 minutes.
Add diced tomatoes and remaining spices (coriander, paprika, turmeric, cayenne, brown sugar). Stir until well incorporated and season with salt to taste.
Gently place stuffed eggplants into the sauce, ensuring they are mostly submerged. Cover and simmer over medium-low heat for 20 minutes until eggplants change color and are cooked through but not mushy.
Add a little water if needed for moisture, but avoid stirring to prevent eggplants from falling apart.
When tender, stir gently, garnish with fresh cilantro, and serve warm with roti, naan, or basmati rice.