In a large bowl, toss tofu strips with some oil,salt and pepper. Marinate for 10-15 minutes.
In a small bowl, stir together rice vinegar, soy sauce, dark soy sauce, Ketchup and cornstarch. Set aside.
Heat a large frying pan over high heat. Add 1 tbsp oil. Arrange the tofu strips in a single layer. Let it cook undistuerbed on meduim-high heat for 1-2 minutes. Flips the strips and let it crisp on the other side. The tofu strips should look brown and crisp on both the sides.
Remove and place on a kitchen towel/tissue paper to absorb extra oil.
In the same pan add remaining oil. Once it is hot add in garlic, ginger, and red chili flakes. Fry over low heat for about 10-15 seconds, or until aromatic, taking care not to burn the garlic.
Increase the flame and add Sliced onion. Saute over high heat for a minute. Add red bell pepper and toss in high flame for about 1 minute. Make sure to stir and toss the vegitables well.
Add the crisp tofu strips followed by the prepared sauce. Toss eveything well. Season with salt or pepper if required.
The sauce will start to thicken. If it is very thick add 1-2 table spoons of water. Cook furter for a minute or so.
Garnish with chopped green onions and green chillies.
Serve hot as an appetizer or along with rice or noodles.