ok, so after muddling blindly through the API for hours guessing here and there, I did this, which works but is probably clunky or smells, so please feel free to improve on my own answer.
private MultiWindowTextGUI mwtg;
private BasicWindow bw;
private CheckBoxList<String> checkBoxList;
private List<String> ckeckedItems;
Terminal terminal = new DefaultTerminalFactory().createTerminal();
TerminalScreen screen = new TerminalScreen(terminal);
MultiWindowTextGUI mwtg = new MultiWindowTextGUI(screen);
this.checkBoxList = new CheckBoxList<String>();
this.checkBoxList.addItem("item1");
this.checkBoxList.addItem("item2");
this.checkBoxList.addItem("item3");
this.checkBoxList.addListener((sel, prev) ->
{ this.ckeckedItems = this.checkBoxList.getCheckedItems(); }
);
Panel panel = new Panel();
panel.setLayoutManager(new GridLayout(4));
panel.addComponent(this.checkBoxList);
Button button = new Button("Done", () -> this.bw.close());
button.addTo(panel);
this.bw = new BasicWindow("Choices");
this.bw.setComponent(panel);
this.mwtg.addWindowAndWait(this.bw);
I hope this may be useful for someone...