Heat 1tbsp oil in a pan; add the onions, ginger+garlic paste and cook till the onions turn translucent, about 3~4 minutes.
Next add the spinach, green peas and cook till the spinach is wilted about 3~4 minutes.
Next add the paneer along with the spices (chili powder, ground cumin, ground coriander, garam masala, salt and pepper). Mix well and cook for 3~4 minutes.
Add lemon juice and chopped cilantro. Paneer filling is now ready.
Spread some green chutney on one bread slice. Top it with paneer filling. Spread some ketchup on another slice of bread and place it on the paneer. Press lightly.
Butter the top and bottom of the sandwich and toast it on a hot pan under golden on both sides. Once done, cut the sandwich in half diagonally and serve warm or at room temperature.