Heat 1 tbsp oil in a pan over medium heat. Sauté the chopped red bell pepper until it is cooked, which should take 6-8 minutes. Remove from the pan.
Add another tbsp of oil to the pan. Cook onions for 4-5 minutes until translucent. Add garlic, ginger, and green chili, and cook for 2 minutes.
Add turmeric, coriander, and red chili powder and cook for a minute. Add the tomatoes and ¾ tsp salt.
When excess water from the tomatoes has mostly evaporated, remove the pan from the heat. Let it cool off a little and blend its contents with yogurt or cashew cream.
Pour the gravy back in the pan and keep it over medium low heat. Clean out the food processor with ½ cup water (check gravy consistency; it should be pretty thick) and add the water to the pan. Finish with garam masala, crushed kasoori methi, and salt to taste. Cook for 2-3 minutes.
Drizzle olive oil on one side of two slices of bread and place the oiled side down on a pan over medium heat. Add cheese, sauteed red bell peppers, and ~ 2 tbsp of tikka masala sauce. Top with the other slice of bread, oiled side facing up.
Press the sandwich lightly with the back of a spatula. Flip it when it holds together well (~ 3 minutes) and continue to press it for 3-4 minutes on the other side. Cook until both sides are golden-brown.
Repeat for the remaining slices of bread, depending on how many sandwiches you're making. The tikka masala sauce keeps well in the fridge for up to 5 days and a few months in the freezer, so make extra!