So-Trendy Beef Burgers

1. Combine porcini mushrooms with 1 cup (250 mL) boiling water in small bowl; let stand for 20 minutes. Drain and rinse mushrooms; chop finely and set aside.
2. Heat oil in small skillet over very low heat. Add unpeeled garlic; cook, stirring often, for about 10 minutes or until softened and skins are golden. Remove from skillet; let cool slightly. Squeeze garlic out of skins into large bowl, mashing with back of spoon.
3. Add porcini mushrooms, ground beef, tarragon, salt and pepper to bowl with garlic; lightly combine. Form into four 3/4-inch (2 cm) thick even-sized patties. Grill patties using medium-high heat for 5 to 7 minutes per side, until digital rapid-read thermometer inserted sideways into centre of each patty reads 160°F (71°C). Meanwhile, grill cut sides of buns until lightly golden.
4. Place arugula on bottom halves of buns; top each with cooked patty. Top each patty with piece of goat cheese, tomato slice and bun top.