Heat a large skillet over medium high heat and some oil and butter while working in batches and lightly sear the meat on all sides (I find it saves time to use bigger chunks and allow them to rest then cut into bite-sized pieces, but you can do that in reverse).
Once complete with all the meat, transfer to a large Crock Pot.
Add carrots and onion and cook until soft, then garlic for 1 minute.
Cook tomato paste for 2 minutes, then add red wine and deglaze the pan.
Carefully transfer all the contents to the base of the slow cooker with the seared lamb.
Add in all remaining ingredients except for the flour, water and peas, stir to mix well.
Cover your slow cooker and cook on LOW for 8 hours (high for 4-5), then remove rosemary sprigs.
To thicken, mix ½ cup water in a spouted measuring cup with flour. Then pour it back into the slow cooker and cook for an additional 15-20 minutes but on HIGH.
When ready to serve add in the peas and stir to combine (they will warm up and soften quickly).
Taste and add any additional water as needed.