Place paneer in a bowl and add enough cornstarch to coat; mix well.
Heat oil large skillet over medium heat; fry paneer until golden brown, 1 to 2 minutes per side. Transfer paneer to a paper towel-lined plate, reserving oil in the skillet.
Combine garlic and ginger in the hot oil; add onion, green chile peppers, and bell pepper. Cook and stir until vegetables are golden brown, about 5 minutes.
Mix soy sauce, chile sauce, tomato sauce, sugar, salt, and remaining cornstarch into onion mixture, stirring in water if mixture is too thick. Add paneer; cook and stir until gravy is thickened, 2 to 3 minutes. Remove skillet from heat and garnish chili with cilantro and green onions.