1 package (10 ounces) frozen spinach, thawed and drained
1 can (14 ounces) artichoke hearts, drained and chopped
1/2 cup shredded Monterey Jack cheese
Combine 1-1/2 cups flour, undissolved yeast, sugar and salt in a large mixer bowl. Add water and oil and beat for 2 minutes. Add enough remaining flour to make a soft dough. Turn out onto floured surface and knead 5 to 6 minutes, until smooth. Cover dough and let rest 10 minutes. Combine butter and minced garlic; set aside.
Roll or press dough to fit into a greased 13 x 9-inch pan. Using wooden spoon handle or a finger, poke holes in dough every 1 to 2 inches. Drizzle with garlic butter mixture. Cover and let rise 30 to 40 minutes, until doubled. Bake in a preheated 375°F oven for 20 to 25 minutes; remove from oven.
While focaccia is baking, make the topping. Melt butter in a large skillet over medium heat; add onion and cook 2 to 3 minutes or until onion is softened. Reduce heat to low and add cream cheese, mayonnaise, Parmesan cheese and garlic powder. Stir until cheeses have melted. Squeeze any remaining liquid out of spinach. Add spinach and artichokes to skillet, stirring to blend. Spread over partially baked focaccia. Sprinkle with Monterey Jack cheese.
Return to oven and bake an additional 10 minutes or until cheese is melted. Best served warm.