Place a heavy casserole dish or Dutch oven over medium to medium-high heat. Allow 2–3 minutes for the cookware to fully heat through. The handle should become hot to touch.

Add a generous amount of neutral oil. Place the sausages in a single, uncrowded layer. Do not disturb them for 2–3 minutes to allow proper caramelisation. Once the sausages naturally release from the pan, rotate to brown each side evenly. Treat the sausages as having "four sides" for better browning. When they have a deep golden colour and the thickest part reaches at least 67°C, remove and set aside.

Lower the heat slightly. Skim off excess fat if necessary, leaving enough to coat the vegetables. Add sliced green peppers first and season lightly with salt. Cook until wilted and softened, about 5–7 minutes, allowing them to deglaze the pan naturally. Then add the sliced onion and jalapeño (if using) and continue to cook until softened. Stir in the chopped garlic and sauté for another 1–2 minutes.

Pour in the soy sauce, scraping the bottom to lift all the flavourful browned bits (fonds). Add the drained black beans and stir well, coating them with the flavoured oil and vegetables. Let them sauté briefly to evaporate any surface moisture.

Add enough water (or stock) to just cover the ingredients. Bring to a gentle boil, taste, and adjust the seasoning with additional salt and pepper if needed (bearing in mind the saltiness of the sausages and soy sauce). Cover and simmer for at least 10 minutes to allow the flavours to meld.

At this point, you can either: Quick Version: Nestle the browned sausages back into the casserole, heat through for 5–10 minutes, and serve. Slow-Roasted Version: Transfer the uncovered casserole to a preheated 150°C oven and bake gently for 30–60 minutes. Top up with water occasionally if needed. Add sausages back in 10 minutes before serving to warm through.