Kansas City Steak & Spinach Salad

• 3 oranges
• 1 garlic clove
• 350 gr tender beef steak (boneless)
• 60 gr mushrooms (fresh)
• 60 gr spinach (fresh)
• 60 ml vegetable oil
• 45 ml wine vinegar (red)
• 45 ml kikkoman lite soy sauce divided
• 1 gr black pepper
• 1 gr oregano