Mushroom Rice

2 – 3 tbsp olive oil , separated
30g / 2 tbsp butter
750g / 1.5 lb slices mushrooms OR one can of cream of mushroom soup
2 garlic cloves , minced
1 small onion , finely diced
1 1/2 cups long grain rice, uncooked
2 1/4 cups vegetable stock / broth (or chicken)
1 1/2 – 2 cups green onions , sliced
Optional: More butter to stir through