In a small skillet, saute sunflower kernels and almonds in butter. Cool. Meanwhile, in a jar with tight-fitting lid, combine the oil, vinegar, lemon juice, sugar, salt, mustard and garlic; shake well. In a large salad bowl, toss the lettuce, oranges, avocado, onions and sunflower kernel mixture. Drizzle with dressing. Serve immediately. Yield: 6-8 servings.