Heat a Dutch oven or large pot over a medium-high heat.
Add the bacon and sauté until crispy, then transfer the bacon to a plate, leaving the bacon grease in the pan.
Pat the lamb meat dry with paper towels, then massage the salt, pepper and garlic powder into it.
Toss the seasoned lamb in flour to coat evenly.
Add a tablespoon of oil to the Dutch oven and heat it over a medium-high heat.
Add the lamb and sear for 3 or 4 minutes per side until golden brown all over, working in batches so you don’t overcrowd the pot. Add more oil between batches if needed.
Transfer the lamb to a plate.
Turn the heat down to medium and sauté the onions in the same pot for 5 minutes or until almost translucent.
Add the garlic and cook for another minute or 2 until fragrant.
Add the Guinness, tomato paste, bay leaves, and thyme leaves, stirring to combine.
Add the bacon and lamb back into the pot and bring the mixture to a boil.
Turn it down to a simmer, cover the pot and simmer gently for 1 ½ hours or until the lamb is starting to become tender.
Add the carrots and potatoes and submerge them in the sauce.
Cover and cook for another 20 to 25 minutes or until the vegetables are tender.
Stir in the thawed peas and let the lamb stew rest for 5 minutes.
Ladle the Irish stew into bowls, garnish with fresh parsley or thyme if liked, and serve.