Spicy Sesame Rice Bowls

Name: Spicy Sesame Rice Bowls
Ingredients: 1/3 c. Korean red pepper paste (gochujang); 2 tbsp. toasted sesame oil; 1 tbsp. soy sauce; 1 tbsp. sugar; 3 cloves garlic, crushed with press; 1 lb. beef top round, cut against grain into very thin 2-long slices; 12 oz. medium shiitake mushrooms, stemmed; 1 seedless (English) cucumber, thinly sliced; 1/4 c. rice vinegar; 5 oz. baby spinach; 6 c. cooked white rice, hot; Thinly sliced green onions, shredded carrots, kimchi and sesame seeds for serving