Whisk 1/2 cup cream, 1 tablespoon lemon juice and 1 teaspoon salt in bowl. Combine chicken and cream mixture in large zipper-lock bag; refrigerate 30 minutes.
Heat oil in large skillet over medium-high heat until shimmering. Cook onion until golden, about 3 minutes. Add mushrooms, bell pepper, 1/4 teaspoon salt, and pepper and cook until vegetables have softened, about 5 minutes. Stir in flour and cook 1 minute. Add Madeira, scraping up any browned bits with wooden spoon, and cook until thickened, about 1 minute. Add broth and remaining cream and cook until sauce is very thick and spatula leaves trail when dragged through sauce, about 5 minutes.
Stir in chicken mixture and reduce heat to medium-low. Simmer, stirring frequently, until chicken is no longer pink, about 10 minutes. Off heat, stir in remaining lemon juice and parsley. Serve with toasted bread.