Preheat oven to 425°F and line a large baking sheet with parchment paper.
Place cauliflower florets in a large bowl. Add soy sauce, garlic powder, onion powder and avocado oil and toss until well combined.
Add cornstarch to the bowl and toss again until each floret is evenly coated.
Spread the cauliflower out onto the prepared baking sheet in an even single layer. Bake for 15-20 minutes, tossing halfway through until cauliflower starts to brown around the edges. Turn oven to broil and broil for about 3 minutes until edges/top of cauliflower start to get crispy and brown.
While cauliflower cooks, make the sauce by combining ketchup, soy sauce, maple syrup, vinegar, sesame oil, garlic and ginger in a bowl. Whisk together until combined.
In a separate bowl, add the cornstarch to the water and stir until cornstarch is dissolved. Add the mixture to the sauce and stir again until combined.
Place a large non-stick skillet over medium heat.
Once hot, add the peppers and pineapple and let cook for 2-3 minutes until just slightly softened.
Add the prepared sauce, reduce heat to medium-low and simmer while stirring until sauce becomes thick, about 1-2 minutes.
Add cauliflower florets to the skillet, toss well until fully coated in the sauce.
Garnish with chopped green onions and sesame seeds and serve immediately.