Heat the olive oil in a cast-iron skillet on medium-low.
Sautee your peanuts and cashews in this oil.
Add your least tender vegetable first, and let it cook until slightly softened before mixing in your next set of vegetables to cook. In this manner, add vegetables set by set until all of them have been incorporated.
In the meantime, whisk together the soy sauce, garlic, brown sugar, sesame oil, water, and cornstarch in a small bowl.
Once all vegetables have been cooked to your desired tenderness, mix in the sauce made in step 3 to the skillet and cook until sauce has thickened.