To make the marinade, combine the olive oil, Worchestershire sauce, Dijon mustard, garlic, and herbs.
Put tri-tip roast in a large zip-topped bag and add marinade. Close bag and use your fingers to work the marinade over the roast. Chill in the fridge for at least 6 hours and up to 24 hours.
Preheat oven to 425°F and grease a medium roasting dish or rimmed pan with nonstick spray. Add roast to prepared pan and sprinkle generously with salt and pepper.
Roast tri-tip for about 30-40 minutes, or until a reads 135-140°F for medium-rare. Remove roast from pan, set aside and cover with foil.
Reduce oven to 375°F. Add butter to roasting pan and let melt. Add mushrooms and toss to coat with butter. Sprinkle with salt and pepper. Roast mushrooms for 10-15 minutes, until browned and fragrant.
Slice tri-tip roast and serve with mushrooms.
Calories: 526kcal, Carbohydrates: 5g, Protein: 49g, Fat: 34g, Saturated Fat: 12g, Cholesterol: 162mg, Sodium: 231mg, Potassium: 1044mg, Fiber: 1g, Sugar: 1g, Vitamin A: 206IU, Vitamin C: 3mg, Calcium: 90mg, Iron: 4mg