In a medium saucepan, heat 1 tablespoon olive oil over medium-high heat. Add the barley and garlic and cook, stirring, until toasted, about 3 minutes. Add 2 1/2 cups water and 1/2 teaspoon salt and bring to a boil. Cover, lower the heat and simmer until the water has evaporated, 35 to 40 minutes.
Meanwhile, in a large skillet, toast the breadcrumbs over medium heat for 7 minutes. Transfer to a plate. Add 2 tablespoons olive oil to the skillet and heat over medium-high heat. Add the squash and cook until browned, about 6 minutes. Add the kielbasa and cook until the sausage is browned and the squash is tender, 5 minutes. Transfer to a large bowl.
Return the skillet to medium-high heat and add the remaining 3 tablespoons olive oil. Add the cauliflower and 2 tablespoons water; season with salt and pepper. Using a second skillet, weigh down the cauliflower until browned on one side. Turn and cook until tender, about 5 minutes. Add to the kielbasa and squash. Stir in the barley and parsley; top with the breadcrumbs.