Learn Turkish: Sebzeleri kısa süre haşlayalım, yani çok yumuşak olmasınlar. - Let's boil the vegetables for a short time, meaning they shouldn't be very soft.

Here, yani acts as a clarifier meaning "in other words" or "meaning." It doesn't mean "therefore" as a logical result; instead, it rephrases the first instruction (kısa süre haşlayalım) to clarify what the desired outcome actually is (the vegetables not being too soft). It's a very natural way to add a self-correction or clarification mid-thought.

Why do we switch from "let's" (haşlayalım) to the third-person imperative (olmasınlar)?

In the first clause, the speaker is suggesting an action for "us" (haşlayalım). In the second clause, the subject changes to the vegetables. Olmasınlar is the third-person imperative ("let them not be" or "they shouldn't be"). In Turkish, the third-person imperative is frequently used to express how things should or must be, even for inanimate objects like vegetables!

Why is sebzeleri in the accusative case here instead of just being sebzeler?

Because the vegetables are a specific, known group being acted upon (the ones you are about to cook). If you said sebze haşlayalım, it would mean "let's boil [some/any] vegetables" as a general activity. The -i suffix makes it a definite direct object, showing we are talking about these specific vegetables.

Could we say kısa bir süre instead of just kısa süre?