Jalapeno Pesto Pasta

Ingredients:

Pasta – 16 oz (Penne or your preference – cooked according to package directions)
Baby Bella Mushrooms – 12 oz, sliced
Onion – 1 small, sliced
Red Bell Pepper – 1/2, sliced
Olive Oil – 4 Tbsp, divided
All-purpose Flour – 2 Tbsp
Milk – 1 1/2 cups
Jalapeno Basil Pesto – 2 Tbsp (or any pesto)
Salt – to taste
Black Pepper – 1/4 tsp