Bring peas and 8 cups of the water to boiling in a large pot. Remove from heat and let soak 1 hour (or soak peas in 8 cups cold water overnight). Drain, rinse and return to pot. Cover with 8 cups fresh water and bring to boiling. Reduce heat and simmer, covered, about 30 minutes or until peas are tender. Drain and transfer to a large bowl.
Meanwhile, in a blender combine the shallot, oil, vinegar, sugar, Dijon, salt, Italian seasoning, black pepper, and cayenne, if desired. Cover and blend until smooth.
Pour dressing over warm peas in bowl. Cover and let peas cool in the dressing, stirring occasionally. Stir in sweet peppers, green onions, and pimientos.