Peel potatoes. Cut into evenly sized 1/2-inch cubes. Add potatoes to a large stockpot of water; bring to a boil. Once boiling, lower heat to a simmer and continue cooking until potatoes are fork tender. Drain; set aside.
While potatoes are cooking, add buttermilk, butter, spices and half of the cheese in a small saucepan. Heat slowly over low heat until cheese and butter have melted, stirring frequently.
Add drained potatoes to a large casserole dish, half of the cooked bacon and half of the green onions. Pour buttermilk mixture over the top. Fold in peas. Top with remaining cheese, bacon and green onions. Bake uncovered at 375 degrees for 20 minutes.