Heat 1 tbs olive oil and the butter in a large, ovenproof skillet or Dutch oven over medium-high heat. Working in batches to avoid crowding, sear the lamb cubes until browned on all sides, about 3–4 minutes per batch. Transfer browned lamb to a plate and set aside.

Sauté vegetables

Add remaining 1 tbs olive oil to the same pot. Add diced onion and sauté 4–5 minutes until translucent. Add minced garlic and cook 30 seconds until fragrant. Stir in sliced peppers and mushrooms and cook 5–6 minutes until they begin to soften and release juices.

Build the sauce

Return browned lamb to the pot. Stir in tomato paste and cook 1 minute. Add tomato passata (or crushed tomatoes), stock, dried oregano, thyme, smoked paprika, bay leaf, and remaining 1/2 tsp salt. Bring mixture to a gentle simmer, scraping any browned bits from the bottom.

Bake

Cover the pot with a lid or foil and transfer to the preheated oven. Bake 1 hour, then check tenderness. If lamb is nearly tender, remove lid and bake uncovered 15–20 more minutes to reduce sauce slightly. Total cooking time in oven will be about 1¼–1½ hours depending on lamb. If sauce reduces too much, add up to 1/4 cup water or stock.

Finish

Remove bay leaf. Taste and adjust seasoning with remaining salt and pepper as needed. Sprinkle chopped fresh parsley over the casserole before serving.

Rice

While the casserole is in the oven (about 20–25 minutes before serving), rinse the rice under cold water until the water runs clear. In a small saucepan bring 2 cups water to a boil with 1 tsp salt and 1 tsp butter or oil. Add rice, stir once, cover, reduce heat to low and simmer 15 minutes without lifting the lid. Remove from heat and let stand covered 5 minutes. Fluff with a fork before serving.

Salad

Just before serving, toss salad greens, cherry tomatoes, cucumber slices and red onion in a bowl. Whisk together 2 tbs olive oil, 1 tbs red wine vinegar, 1/4 tsp salt and 1/4 tsp pepper; drizzle over salad and toss to combine. Serve immediately alongside the casserole and rice.