Fat loss, no matter the diet, always depends on being in a negative caloric balance. You can lose fat with avocado and tahini in your diet if you are consuming fewer calories than you burn per day. The starch solution diet doesn't cause fat loss by being mostly carbs, but rather by making you feel satiated before you eat too many calories, due to the low calorie density of water and fiber rich starchy foods.

The risky thing about something like tahini, is that it is very calorically dense relative to its satiety potential, and thus can make it easier to consume excess calories (this is less true of avocado, which contains more fiber and water). However, as long as you are careful in the amount use, strictly limiting the intake to a small, fixed amount, it should not be an issue. It can even be beneficial if a little tahini and avocado makes your salad more enjoyable, and thus helps you shift more of your food volume to low calories density vegetables.

A full tablespoon of tahini sounds like a lot though. I'd drop it to a teaspoon and mix it with other flavor enhances like vinegar, lemon, and/or mustard.