One-Pot Creamy Vegetable Soup

Heat oil in a large heavy pot over medium-high heat. Add onion; cook, stirring occasionally, until softened, about 5 minutes. Add garlic; cook, stirring constantly, until fragrant, about 1 minute. Add flour; cook, stirring constantly, until toasted, about 1 minute. Add milk, broth, potato, lima beans, salt and pepper; stir to combine. Bring to a boil over medium-high heat. Reduce heat to maintain a simmer; cook, stirring occasionally, until the potatoes are tender, about 20 minutes. Stir in mixed vegetables, peas, dill and lemon zest; cook, stirring often, until warmed through, about 4 minutes. Serve hot.