Cook rice or rice noodles according to package directions.
Make the tofu
Press a block of firm tofu in a tofu press or between two cutting boards with a heavy pot on top. Cut the tofu into the desired shape. (I used triangles, but you can cut them into squares or cubes.)
Place 1/3 cup of cornstarch mixed with 1/2 teaspoon of salt into a dish, then coat the tofu in the cornstarch mixture. (This will make the tofu extra crispy, but you can omit this step if you would like.)
Heat a large skillet with 3 tablespoons of oil over medium-high heat. Place the pieces of tofu in the hot oil and allow to cook for about 5 minutes before flipping. (Allow them to cook in the oil without touching them until they move freely when you shake the pan and start to get golden brown.)
Flip the tofu and allow it to cook on the other side for about 5 more minutes.
Make the sticky sauce
While the tofu is cooking make the sticky sauce by combining 1/3 cup water, 3 tbsp agave nectar, 1 tbsp soy sauce, 1 tbsp corn starch, and 1 tbsp ketchup then stir well. After the corn starch dissolves, add 1 tbsp sesame oil and stir again. (Add a dash of red pepper flakes if you want a little spice.)
Put it all together
After both sides of the tofu are golden brown and crispy, pour the sauce over top of the tofu and continue to heat until the sauce bubbles and thickens - this will take about 30-60 seconds. Shake the pan around a little to ensure one section doesn't get too hot. At this point, your sauce will be thick and glossy.
Serve your sticky tofu over a bed of rice or noodles and sprinkle with green onions.
Notes
*Nutrition values include the sticky tofu served over 1 cup of white rice.