In a large heavy saucepan, heat oil over medium-high heat. Add onion and garlic and sauté 5 minutes or until tender. Stir in potatoes, tomatoes, bouillon cube and 3 cups cold water and bring to boil. Reduce heat and simmer, covered, stirring occasionally, 15 minutes or until the potatoes are tender.
Stir in salmon, dill, salt and pepper. Simmer uncovered, 3 minutes or just until salmon is opaque. Stir in milk and simmer 2 minutes or until heated through. Remove salmon chowder from heat and stir in lemon juice.