Heat a skillet with olive oil, sauté mushrooms, red pepper, shallot, and garlic until soft (about 10 minutes). Combine sour cream, cream cheese, lemon zest, juice, mustard, artichokes, and the cooked veggie mix in a slow cooker.
Top with 4 oz Swiss cheese. Cook covered on low for 2 1/2 to 3 hours, stirring occasionally, until the mixture is gooey and well combined. Serve with sliced baguette, crackers, or veggies for dipping.