In a mixing bowl, combine unsweetened plant-based yogurt, Kashmiri red chili powder, turmeric powder, and salt.
Cut the Soya Chaap into 1-inch (2.5 cm.) thick slices, discarding the stick in the center if there is one. Mix the slices into the marinade, ensuring they are well coated. Set them aside to marinate under refrigeration for at least 4 hours or overnight.
In a blender, add quartered tomatoes, garlic cloves, diced onion, grated ginger, Kashmiri red chili powder, turmeric powder, coriander powder, the sweetener of your choice (jaggery, coconut sugar, palm sugar, or brown sugar), and unsweetened plant-based yogurt. Blend the ingredients until you have a smooth paste.
In a thick-bottomed pot or dutch oven, heat cooking oil over medium heat for 90 seconds. When the oil is hot, add the marinated Soya Chaap pieces to the pan. Cook them until they develop a golden brown color, turning them occasionally. This should take about 7-9 minutes.
Add the ½ cup of onion along with the garam masala, fenugreek leaves, chopped cilantro, and salt. Continue to sauté for 4 minutes until the onions become fragrant.
Pour the blended mixture into the pan with the Soya Chaap. Stir well to combine. Continue to simmer for an additional 6-8 minutes, allowing the gravy to thicken.
In a small pan, heat cooking oil for the tadka (tempering) over medium heat. Add mustard seeds, cumin seeds, grated coconut, and curry leaves. Let them sizzle and infuse the oil with their flavors for about 90 seconds until you hear the seats popping and sputtering.
Place the soya cheap into an attractive serving dish, pour the tadka over it, and garnish with fresh cilantro leaves.