Let's say an atheist defines themselves expressly as 'lacking a belief in God's existence' as opposed to 'believing God doesn't exist'. Very common move, usually deployed in an attempt to avoid any and all proof burdens. Normally arguments over this devolve into historical arguments over the usage of the term 'atheist', but I think there's a more productive way to deal with people who make this move.
Just ask them whether they believe evolution is guided.
Consider the following:
God is (for the purpose of this argument) defined as omniscient or omnipotent.
If God is omniscient or omnipotent, then it trivially follows that all physical processes were foreseen and orchestrated by Him in advance.
Evolution is cast as just another physical process.
Ergo, if God exists, then evolution is guided.
Ergo, if someone lacks belief in God's existence - if they neither believe 'God does not exist' or 'God exists' - then they cannot believe that evolution is unguided. At best, they can lack belief that evolution is guided.
On the flipside, if they believe evolution is unguided, then they're going to have to provide evidence for this claim - and that is going to be directly tied up in the claim 'God does not exist.'
I think this move works even if God is reduced to merely 'powerful and knowledgeable', so long as God (or any agent) can in principle affect and determine the course of evolution. Mere lack of belief in God(s) leaves the question of guidance wide open with regards to evolution, but if one commits to evolution being unguided, they are committed to arguing against God's existence. And that would mean we're right back where the atheist did not want to be - in the realm of making claims and having a burden of proof.
I think few atheists are going to be willing to swallow the pill of admitting that, for all they know, evolution is guided - and that they merely lack belief in guidance.