Heat butter and a teaspoon of oil in a pan. Add minced garlic and saute till the garlic is a light golden brown.
Add green chillies and onions to the pan and cook till the onions are translucent. To this, add tomatoes, red chilli powder, coriander powder, turmeric powder and salt. Mix well. Cover and cook till the tomatoes break down and turn pasty. This should take about 7-10 minutes.
While the tomatoes are cooking, add a teaspoon of oil to a non stick pan and add the paneer cubes, making sure not to crown the pan. Flip when the bottom is brown. Once both sides are golden brown, take the paneer out on a plate. This step is optional and you can skip it and use the paneer as is.
Add spinach and arugula leaves (or mustard greens if using) and mix well. Cook for 10 minutes till the leaves are cooked through. Mix in kasuri methi (dried fenugreek leaves) and cream. Add paneer, mix gently and serve immediately.