Preheat oven to 425 degrees Fahrenheit (220 degrees Celsius).

Place rinsed and dried salmon fillets in a baking pan; sprinkle with lemon juice.

Combine sauce ingredients in a small mixing bowl and smear it over the tops and sides of the salmon.

Heat a little oil in a medium-size frying pan. Add the red onion and sauté for five to seven minutes over medium heat, until golden and soft. Add the remaining vegetables and sauté, stirring often, until softened. Stir in the salt.

Top the salmon with generous spoonfuls of the vegetable mixture.

Bake for 20 minutes, then broil for two to three additional minutes.

Serve hot or at room temperature.