Step 1 Heat half the olive oil in a large saucepan, which has a lid, over medium–high heat. Cook pork, in batches, for 5 minutes, or until browned, then transfer to a bowl.
Step 2 Heat remaining olive oil in same saucepan. Add onions, garlic and thyme with all mushrooms; stir for 5 minutes, or until onion softens. Return pork to pan with Marsala and cook, stirring, for 30 seconds.
Step 3 Add tomato paste and stock to pan; bring to the boil. Reduce heat, cover pan and simmer for 1 hour, 30 minutes; uncover and simmer for 30–35 minutes, or until pork and potatoes are tender.
Step 4 Meanwhile, cook green beans in a saucepan of boiling water for 2 minutes (until just tender); drain. Serve stew with green beans.