Can I become slimmer with only having fruits for breakfast and dinner but having a normal lunch?

Balanced diet. One should always have a balanced diet. To lose weight one needs to have portion control and to exercise. As a general rule, a salad-sized plate should be filled halfway with vegetables, 1/4 with lean protein the size of a deck of cards, 1/4 with complex carbs. One should try to exercise for 30 min 3-5/wk, or walk 10, 000 steps a day. Too many fruits may aggravate Insulin resistance.
More variety. Fruits can have a high glycemic index, i.e. They are very sugary & can stimulate Insulin output. One of the effects of Insulin is to increase accumulation of fat in adipose cells. It's better to eat a mix of complex carbohydrate, protein and fat in small meals throughout the day. Frequent small meals will stimulate your metabolism; not eating conserves calories as your body thinks it's starving.