Slice the ends of the zucchini and discard or compost. Cut remaining zucchini into 1/4-inch thick slices. Place sliced zucchini into a medium bowl.
Cut shallot into 1/4-inch thick slices.
Heat olive oil and butter in a large deep sided skillet over medium-high heat until butter is foamy.
Add minced garlic and saute for 1 minute. Add shallots to the pan and cook for 1 minute.
Add zucchini to the pan and toss to combine all ingredients. Season with garlic salt and black pepper.
Continue cooking, tossing the vegetables occasionally, until zucchini is tender and beginning to brown.
Notes
When choosing zucchini at the store or farmer’s market, look for zucchini that are about 6-8 inches long. That’s a good mature size without being overgrown. Overgrown zucchinis are certainly edible, but they tend to become tough and fibrous. They should be firm to the touch and the skin should not contain and cuts or blemishes.
Store leftovers in an air-tight container kept in the refrigerator for up to 3 days. Reheat in the microwave or on the stovetop with extra butter or olive oil.