Cook the bacon
In a large heavy skillet over medium heat, cook the bacon until cooked through but not crisp, 6–7 minutes. Transfer to a plate, leaving the bacon fat in the skillet.
Brown the chicken
Season the chicken with the salt and pepper. Increase the heat to medium-high and cook the chicken in a single layer in the bacon fat until browned and just cooked through, about 4 minutes per side. Transfer to a bowl, leaving any juices in the skillet, and cover loosely with foil to keep warm.
Build the base
Add the vegetable oil to the skillet, then add the onion. Cook, stirring, adding ¼ cup of the chicken stock midway and scraping up any browned bits, until softened and lightly browned, 3–4 minutes.
Add aromatics
Stir in the garlic and jalapeño and cook until fragrant, about 2 minutes.
Cook the vegetables
Add the bell pepper, snow peas, and remaining ¼ cup chicken stock. Cook, stirring, until the vegetables begin to soften, 3–4 minutes.
Finish the stir-fry
Return the chicken (and any juices) to the skillet along with the pineapple and stir fry sauce ingredients. Cook, stirring, until the sauce bubbles and thickens slightly, about 3 minutes. Stir in the cashews and reserved bacon.
Serve
Divide among bowls, garnish with scallion greens if using, and serve hot over white rice.