Heat 1 teaspoon oil on a tawa over medium. Add the green chillies and garlic. Blister 2 to 3 minutes, turning, until the skins wrinkle and smell roasted, not raw.
Pound in a mortar with salt, roasted peanuts, and coriander until coarse. You should still see peanut bits. If you use a blender, pulse 4 to 5 times. Do not run it into a puree.
Taste. If it is too hot, add 1 more tablespoon peanuts. Do not add water.
Sear the paneer
Heat 1 tablespoon oil in a skillet over medium-high. Lay the paneer slabs in a single layer. Cook 2 minutes per side until gold spots appear and the center is still soft.
Take the pan off the heat. Toss the hot paneer with 2 tablespoons thecha and a pinch of salt. Coat, do not mash. Overcooked paneer turns rubbery. Get it off the heat as soon as the spots show.
Assemble and toast
Spread a thin layer of hung curd on the inside of each bread slice. This is the heat buffer and the moisture barrier.
Lay 2 thecha-coated paneer slabs on 4 slices. Add a thin cheese slice if you want. Spread a little extra thecha if you like more heat. Close the sandwiches.
Butter the outsides. Heat a tawa over medium, not high. Toast 2 to 3 minutes per side until the bread is deep gold and the paneer is warm in the middle. Rest 1 minute, then cut.
Notes
Start with 3 chillies if you do not know your batch. Add thecha on the inside later.For kids, keep the extra thecha off their sandwich and use a thicker yogurt smear.Hung curd, not regular dahi. Regular curd wets the bread.Store leftover thecha in a small jar in the fridge for up to 5 days. Use it in the thecha paneer bowl.Store the paneer filling, seared and coated, in an airtight box for 2 days. Assemble and toast fresh.The finished sandwich is best off the tawa. Reheat leftovers on a hot tawa, 1 minute a side. Skip the microwave. It makes the bread chewy.