Peel and rinse shrimp; pat dry; mix with creole seasoning; set aside. Crush tomatoes by hand and place in a strainer and set aside. Reserve liquid.
In a heavy Dutch oven, heat butter over medium heat until bubbling; add the yellow onions, bell pepper and celery. Sauté for about 20 minutes until starting to caramelize.
Add the garlic and about half of the Herb and Spice Blend (not the bay leaves yet) and about ⅔ of the green onions. Mix well and sauté until aromatic - about 2 minutes.
Mix in the AP flour and stir thoroughly. Cook about 2 to 3 minutes stirring constantly so it does not stick.
Add the crushed tomatoes and tomato sauce and mix well. When it starts to simmer, add about half of the remaining Herb and Spice Blend, both bay leaves, the sugar and Worcestershire sauce. Mix well.
Add in 2 tablespoons of lemon juice, the lemon slices and one cup of the shrimp stock (reserve the remaining stock). Mix well and bring back to a heavy simmer; lower the heat to a slight simmer and cook for 30 minutes uncovered, stirring often while it thickens.
After 30 minutes, cover the dutch oven and continue to cook on low for another 30 minutes, stirring often so it does not stick. We are looking for a thick, smooth (but chunky) sauce, so remove the cover or leave the cover on, depending on how the thickening is coming along. If it gets too thick, add some of the reserved stock, if its not thick enough simmer with the cover off.
At this point taste for seasoning. Add more if needed but remember that the shrimp will soak up a lot of the seasoning and salt so its fine if it seems over seasoned at this point. See Notes
Increase the heat to med/high until just starting to simmer then add the shrimp. Mix well. Cover the dutch oven and cook for 5 minutes then turn off the heat and let sit for 5 more minutes, still covered.
Remove the bay leaves and lemon slices. Serve over rice sprinkled with green onions on top.